Shortstopping vinyl chloride polymerizations with polyunsaturated monocarboxylic acids



solute pressures.

Patented Nov. 4, 1952 UNITED STATES PATENT OFFICE SHORTSTOPPING VINYL CHLORIDE POLY- MERIZATIONS WITH POLYUNSATURATED MONOCARBOXYLIC ACIDS Meyer H. Danzig, Naugatuck, Conn., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. Application July 10, 1951, Serial No. 236,074

12 Claims. (01. 260---92.8)

' polymerization, as is well known, may be an emulsion polymerization (see Mark et al. U. S. Patent 2,068,424, and German Plastics Practice by De- Bell, Goggin & Gloor, pub. by DeBell and Richardson, Springfield, Mass, 1946, pages 57-66), or a granular polymerization (see Lightfoot U. S. Patent 2,511,593, and German Plastics Practice, pages 6643, and the article by Ruebensaal on Vinyl Resins in Chemical Engineering for December 1950, vol. 57, pages 102 to 105).

After conversion of the desired amount of monomer to polymer, residual unreacted monomeric vinyl chloride is removed and the polyvinyl chloride collected by various means, such as by coagulation or spray drying in the case of aqueous emulsion polymerization, or by filtration in the case of aqueous granular polymerization. The resulting polyvinyl chloride is usually washed with water and dried. If the polymerization goes beyond the desired conversion, a polymer having properties inferior to those desired in the final product may result, particularly as regards heat and light stability. To avoid this, the batch is generally cooled after the desired conversion. Undesirable post-polymerization may also take place in the blow-down tank or in the stripper where unreacted vinyl chloride monomer is removed. At the end of the polymerization, it may be necessary to store or hold the polymer batch for some time without cooling before removing unreacted vinyl chloride monomer. In this case the polymerization may continue during storage and thus give a product of too high conversion and of resultant undesirable properties. Also, when the unreacted vinyl chloride monomer is removed from the aqueous medium, there may be some vinyl chloride monomer, adsorbed on the polyvinyl chloride particles in the aqueous medium, which is not removed until drying of the polyvinyl chloride. This adsorbed vinyl chloride monomer may polymerize on the polyvinyl chloride particles before it can be removed, ad-

.. azo catalyst.

versely afiecting the properties of the finally recovered polyvinyl chloride. It is therefore desirable to add a material which acts to terminate or shortstop the vinyl chloride polymerization reaction after the desired partial conversion of polymerizable monomer to polymer has taken place and to prevent any further polymerization of the residual unreacted vinyl chloride monomer.

I have found that polyunsaturated carboxylic acids are efiective shortstopping agents for vinyl chloride polymerizations.

.In carrying out the present invention, the-polyunsaturated carboxylic acid is added to the polymerizationreaction afterpartial conversion of polymerizable monomer to polymer (usually after about to conversion) and thereafter the unreacted vinyl chloride polymer is removed from the aqueous medium, and the polyvinyl chloride recovered in the usual manner. Examples of polyunsaturated carboxylic acids that may be used are sorbic acid, furylacrylic acid, linoleic acid, linolenic acid, eleostearic acid, soybean oil fatty acids, beta vinyl acrylic acid, geranic acid, dehydrogeranic acid, and mixtures thereof. It is noted that monoolefinic carboxylic acids, e. g. acrylic acid, do not shortstop vinyl chloride polymerizations. Small amounts of such polyunsaturated carboxylic acids may satisfactorily be used to shortstop the polymerization reaction, the amount efiective to shortstop the polymerization generally being less than 2% based on the original vinyl chloride monomer used. For practical purposes,-the amount of shortstopper may be between 0.3% and 1% by weight of the original vinyl chloride monomer used.

The polymerization reaction is carried out in the presence of a conventional free radical type polymerization initiator, such as a peroxygen or Examples of peroxygen catalysts are inorganic peroxides, e. g. hydrogen peroxide and persalts, such as alkali persulfates, alkali perborates, alkali percarbonates; and organic peroxides, e. g. diacetyl peroxide, dibenzoyl peroxide, acetyl benzoyl peroxide, lauroyl peroxide,

'cumene hydroperoxide, tertiary butyl hydroperoxide. Examples of azo catalysts are alpha, alpha-azobisisobutyronitrile, and p-methoxyben- Catalytic amounts from 0.05% to 2% based on the vinyl chloride monomer may be used.

Tests showing the efiectiveness of the chemicals of the present invention as shortstopping agents for vinyl chloride polymerization were carried out according to the following procedure: Into each or a number of crown capped bottles equipped with self-sealing liners was placed a typical granular poly erization recipe (100 parts of liquefied vinyl chloride, 325 parts of water, 0.5 part of lauroyl peroxide, and a small amount of suspending agent) Polymerizations were carried out at 47 C. Two polymerizations served as controls to show the conversions at an intermediate polymerization (about six hours) and at a final polymerlization (about nine hours) without shortstopping agent. At the end of the intermediate and. final polymerization times, monomeric vinyl chloride was immediately vented and percent conversions were obtained. In the test polymerizations, 0.5 part (based on 100 parts of vinyl chloride monomer used) of sorbic acid and of furylacrylic acid was added to separate polymerization bottles at the same time as the intermediate control polymerizations and the heating was continued to the same overall time as the final control polymerization. Vinyl chloride monomer was. then vented, and percent conversions were obtained by weighing the polymer.

Thepercent conversions of monomerto'polymer of. the control after the intermediate and final polymerization times, and the percent conversions at. the final polymerization times where the shortstoppers of the present invention were added at the intermediate conversion times, are shown in the following table:

Conversion ipercent) Shortstopper added at intermediate.

conversion Intermediate Final N'one' (intermediate control) 65' N'one (flnalicontrol) 95 0.5 part'i'urylacrylic' acid Bottle polymerizationssimilar to the above were run at 52 with theiollowing typical -granular polymerization.recipe (lilo-parts. of, liquefied vinyl chloride, 300 parts of water, 0.5 part of lauroyl peroxide and a small. amount. of. suspending agent). Intermediate polymerization times were six and one-half hours and final. polymerization times were tenand one-half hours. Results. are shown inthe follclwing table:

Conversion: (percent) Shortstopper added" at intermediate 7 conversion Intermediate Final None (intermediate. control) v 0.3 part of a mixture of linoleic and linolenic acid The above work sh'owsthat the polyunsaturated carboxylicacidsof thepresent invention are effective-shortstopping agents for vinyl chloride'granu- In: bulk polymerizations, the polymerization reaction is generally stopped at lower conversions, e. g. around 40%. With the short stopping agents of the present invention, the polymerization reaction may be stopped at any desired conversion.

In emulsion polymerizations, it is a simple matter to withdraw a sample from the reaction chamher from time to time and to analyze it for total solids in order to determine the percent conversion. On the other hand, it is almost impossible to follow the conversion in a granular polymerization by sampling, because the polymer formed separates so rapidly that a representative sample cannot be obtained. .Thus other methods of determining the amount of conversion, and thereby the point at which the reaction should be stopped, must be used in following polyvinyl chloride granular polymerizations. For example, the heat evolved in the reaction mixture can be measured and be directly correlated with the extent of conversion via the l nown heat of reaction. Also experience has shown that polyvinyl chloride of good physical characteristics may be obtained by stopping the reaction at the pressure drop which is at the point where the liquid vinylch-loride monomer disappears (see German Plastics Practice, pages 61 and 7-7). In systems where the temperature'in the reactor is automaticallymaintained by regulation of the jacket temperature, the pressure drop will be evidenced by asudden pressure fall. In systems where the pressure in the reactor is automatically maintained byregulation of the jacket temperature; the pressure drop will be evidenced by a. rapid rise in jacket water temperature, whereupon the system is thrown out'of automatic control and coolingwater is, introduced into the jacket resulting in the usual fall of pressure in the-reactor. Such methods other than sample analyses of determining when to'shortstop the reaction at. the desired conversion may be used in emulsion polymerization as well as in granular polymerization. The evolution of heat or the viscosity characteristics may be followed in mass polymerization to determine thepoint at which the shcrtstopping agent should be added.

The following illustrates the use of. the shortstoppers of the present invention in batch aqueous vinyl chloride polymerizations. 'A typical emulsion polymerization recipe which uses a water-soluble catalyst parts of liquefied vinyl chloride, 200 parts of water, 0.2 part of potassium persulfate and 1.5 parts of surface-active emulsifying agent), or atypical granular polymerization recipe using a water-soluble catalyst (100 parts of liquefied vinyl chloride, 300 parts of water, 0.3 part of potassium persulfa-te, and a small amount of buiTering and wetting agents), or a typical granular polymerization recipe using a monomer-soluble catalyst (-100 parts of liquefied vinyl chloride, 300' parts of water, 0.5 part of lauroyl peroxide and a small amount of suspending agent) is agitated in a closed jacketed reaction vessel. The batch is initially heated to the desired reaction temperature between 40" C. and 602 C. and maintained at the desired temperature during the polymerization. The pressure in the reactor at such temperatures will be from 4 to 9 atmospheres until the liquid vinyl chloride is polymerized and the pressure drops. After the. pressure starts to drop and before it drops 2 atmospheres, 0.3 to 1 part of sorbic acid, furylacrylic acid, linoleic acid, linolenic acid, eleostearic acid, soybean oil fatty acids, beta vinyl acrylic acid, geranic acid or dehydrogeranic acid per 100 parts of original vinyl chloride used is added so that undesirable further polymerization is prevented. Alternatively, the shortstopping agent may be added at any desired conversion at the discretion of the operator. When the desired conversion has i been reached and the shortstop added, the batch may be transferred to the blow-down or storage tank, held there any desired length of time, and then transferred to the stripper when desired for removal of residual unreacted vinyl chloride monomer. Finishing operations after residual monomer removal are conventional as described in'the literature references referred" to above. The shortstopping agents of the present invention give a greater uniformity of polymer properties, and also result in polymers having enhanced heat and light stability.

The shortstoppers of the present invention olefinic material which is copolymerizable with vinyl chloride, such as a vinyl alkanoate, e. g.

vinyl acetate, or vinylidene chloride, or an alkyl acrylate, e. g. methyl acrylate, or an alkyl alkacrylate, e. 'g. methyl methacrylate, or an alkyl maleate, e. g. dimethyl maleate, diethyl maleate, isobutyl maleate, andmixtures there- 01. Such polymerizations are similar to the homopolymerization of polyvinyl chloride but with a somewhat broader range of reaction temperatures from 0. to 100 (3., depending on the particular vinyl chloride copolymer being made '(see German Plastics Practice, pages '76-'78). The same amount of shortstopping agent based on the amount of vinyl chloride employed may be added after partial conversion, generally at about 60% to 95% conversion of polymerizable monomeric material to polymeric material.

In view of the many changes and modificationsthat may be made without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection afforded the invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of polyunsaturated monocarboxylic acid to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

2. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of carboxylic acid selected from. the group consisting of sorbic acid, furylacrylic acid, linoleic acid, linolenic acid, eleostearic acid, soybean oil fatty acids, beta vinyl acrylic acid, geranic acid, and dehydrogeranic acid to the reaction mixture during polymerization to stop the same after 6 partial conversion of polymerizable monomeric material to polymeric material.

3. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of linoleic acid to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

4. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of linolenic acid to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

5. In the process of preparing polyvinyl chloride by the polymerization of vinyl chloride in an aqueous medium, the step comprising adding 0.3% to 1% of polyunsaturated monocarboxylic acid based on the weight of the original monomeric vinyl chloride used to the reaction mixture during polymerization to stop the same after about 60% to conversion of vinyl chloride monomer to polyvinyl chloride.

6. The method of preparing a vinyl chloride polymer which comprises subjecting material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride to polymerizing conditions in an aqueous medium in the presence of a polymerization catalyst, and after about 60% to 95% conversion of polymerizable monomeric material to polymeric material adding to the polymerization reaction 0.3% to 1% based on the weight of the original monomeric vinyl chloride used of polyunsaturated monocarboxylic acid to stop polymerization of unreacted polymerizable monomeric material, and thereafter removing unreacted polymerizable monomeric material from the aqueous medium.

'7. The method of preparing a vinyl chloride polymer which comprises subjecting material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by Weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride to polymerizing conditions in an aqueous medium in the presence of a polymerization catalyst, and after about 60% to 95% conversion of polymerizable monomeric material to polymeric material adding to the polymerization reaction 0.3% to 1% based on the Weight of the original monomeric vinyl chloride used of carboxylic acid selected fromthe group consisting of sorbic acid, furylacrylic acid, linoleic acid, linolenic acid, eleostearic acid, soybean oil fatty acids, beta vinyl acrylic acid, geranic acid, and dehydrogeranic acid to stop polymerization of unreacted polymerizable monomeric material, and thereafter removing unreacted polymerizable monomeric material from the aqueous medium.

8. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in an aqueous medium in the presence of aperoxygen catalyst, and after partial conversion of vinyl chloride monomer to polyvinyl chloride adding to the polymerization reaction a small amount of polyunsaturated monocarboxylic acid to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

9. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in the presence of a peroxygen catalyst in an aqueous medium at a temperature between 40 C. and 60 C. under a pressure substantially equal to saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of polyunsaturated monocarboxylic acid to stop polymerization of unreacted vinyl chloridemonomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

10. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in .a closed vessel in the presence of a peroxygen catalyst in an aqueous medium at a temperature between40 C. .and 60 C. under a pressure substantially equal to its saturated vapor pressure of about i to 9 atmospheres, and after the pressure begins to drop and before ithas dropped 2 atmospheres adding to the polymerization reaction a small amount of carboxylic acid selected :from the group consisting of sorbic' acid, furylacrylic acid, l-inoleic acid, .linolenic acid, eleostearic acid, soybean oil fatty acids, beta vinyl acrylic acid,

'8 geranic acid, and dehydrogeranic acid to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

11. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in the presence of a peroxygen catalyst in an aqueous medium at a temperature between 40 C. and C. under a pressure substantially equal to its saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of linoleic acid to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

12. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in the presence of a peroxygen catalyst in an aqueous medium at a temperature between 10 C. and 60 C. under a pressure substantially equal to its saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of linolenic acid to stop polymerization of unreacted vinyl chloride monomer,.and thereafter removin unreacted vinyl chloride from the aqueous medium.

MEYER H. DANZIG.

N 0 references cited. 

2. IN THE PROCESS OF PREPARING A VINYL CHLORIDE POLYMER BY THE POLYMERIZATION OF MATERIAL OF THE GROUP CONSISTING OF VINYL CHLORIDE AND MIXTURES OF VINYL CHLORIDE WITH UP TO 20% BY WEIGHT OF THE VINYL CHLORIDE OF OTHER MONOOLEFINIC MATERIAL WHICH IS COPOLYMERIZABLE WITH VINYL CHLORIDE, THE STEP COMPRISING ADDING A SMALL AMOUNT OF CARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF SORBIC ACID, FURYLACRYLIC ACID, LINOLEIC ACID, LINOLENIC ACID, ELEOSTEARIC ACID, SOYBEAN OIL FATTY ACIDS, BETA VINYL ACRYLIC ACID, GERANIC ACID, AND DEHYDROGERANIC ACID TO THE REACTON MIXTURE DURING POLYMERIZATION TO STOP THE SAME AFTER PARTIAL CONVERSION OF POLYMERIZABLE MONOMERIC MATERIAL TO POLYMERIC MATERIAL. 